IGV Temperature Control

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Thread Starter

dontknowman

Hi to all

I'm working on a frame 9 gas turbine with mark4 S.T system which has a boiler (combined cycle). So I have a question. What's the difference between IGV temperature control OFF & ON?
 
B
When Temp. control is <b>on</b>, gas turbine exhaust will be maintained at max temperature, i.e. IGV will be at min possible temp. So when operating in part load then, IGV will be lower and exhaust temp will be higher.

That also means, cooling air flow will be minimized to get high exhaust temp.

This will cause,

1. Low compressor power for less air flow and in turn higher efficiency.

2. at HRSG side you will get higher efficiency because of high exhaust temp.

overall combustion cycle efficiency will increase.

But when gas turbine is in base load or near about it, temp control will not get any extra benefit.
 
If you are in combined cycle mode (GT Exhaust through the HRSG [boiler]), you should have IGV temperature control ON. This will keep the exhaust temperature higher, which will also keep the HP steam temperature higher. If there are exhaust dampers and a bypass stack, the gas turbine control should automatically turn the IGV temperature control OFF and ON based on damper position.

Turning the IGV temperature control off will keep the IGV's full open for most of the gas turbine load range, which reduces the exhaust temperature at part load conditions. I am guessing, based on Mark IV control vintage that this is a 9E, without DLN combustion system (any NOx control would be done with water or steam injection).
 
barindra75,

> When Temp. control is <b>on</b>, gas turbine exhaust will be maintained
> at max temperature, i.e. IGV will be at min possible temp.

When IGV Temperature Control is ON, the IGVs are held at the lowest possible <b>position</b> in order to maximize exhaust temperature.

> 1. Low compressor power for less air flow and in turn higher efficiency.

While the axial compressor might be flowing less air requiring less HP from the turbine section, this actually decreases gas turbine efficiency--because gas turbines are mass flow machines, so the more air they flow the more efficient they are.

> 2. at HRSG side you will get higher efficiency because of high exhaust temp.
>
> overall combustion cycle efficiency will increase.

Overall <b>combined cycle plant thermal efficiency</b> will increase when the gas turbine is at Part Load and IGV Temperature Control is ON. Gas turbine efficiency is down, but the increased exhaust temperature results in higher steam temperature and increased steam production (on some types of HRSGs) which increases the overall combined cycle plant thermal efficiency at Part Load.

When IGV Temperature Control is OFF, the IGVs are opened as a function of speed (except for a short period when the exhaust temperature is around 900 deg F).

There is zero benefit operating a heavy duty gas turbine in simple cycle mode (exhausting to atmosphere--not through an HRSG) in IGV Temperature Control ON during Part Load; in fact, there is a very slight efficiency penalty for doing so.

Once the IGVs reach maximum operating angle, the unit should be at or very near Base Load, and even when IGV Temperature Control is ON (or OFF) the definition of Base Load is when the IGVs are full open (and exhaust temperature is equal to the CPD-biased exhaust temperature control reference).
 
B
Respected CSA,

This is the question I asked several times to me and the machine.
when, air flow is less it means compressor will demand less power. This power would have coming from turbine when temp control mode is ON.
Normally turbine efficiency is, not more than 30%. so the extra air flow will need around three times (of the reduced flow say 15% i.e. 45%) air in the turbine to compensate.

Also in our plant we operated the frame-v machine in both temp control OFF and On mode. When it is ON, efficiency very slightly increase or you can say same.

I will cross check it again, after your comment.
 
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